Publisher Summary This chapter presents an overview of radionuclide imaging technique. Radionuclide imaging demonstrates the distribution of a particular function of an organ and how that distribution of function is altered in disease. It is important to the understanding of radionuclide imaging to be aware that the function of an organ chosen to image the organ with radionuclides is not necessarily the function of the organ that is most relevant to the particular clinical problem at hand. Adrenal imaging with radiopharmaceuticals is a routine procedure in Cushing's and Conn's syndromes. A quantitative approach is more reliable than analog imaging, because of the great variation in depth of adrenals, so that a normal gland that is closer to the skin surface appears larger. Combinations of noninvasive radionuclide and X-ray CT imaging may avoid the need for invasive radiology in most cases. There is no radiopharmaceutical yet available to image insulinomas, glucagonomas, or endocrine adenomas of the intestinal tract. Ovarian imaging is not undertaken because of the potential radiation hazard to germ cells.